In recent years, in association with miniaturization and weight reduction, speeding-up, and multi-functionality of an electronic device, speeding-up and high integration of a semiconductor component have been promoted, and thus, a heat generation density of each element has increased and the local concentration of heat generation has been resulting. In addition, since a variety of resin materials are used in an electronic device-related component, due to the characteristic of the resin material that is the inferiority in heat conductivity, heat generated by the electronic device is caught by a cover or the like made of the resin and is accumulated, thereby leading to the problem in that the temperature increase causes a failure rate of the electronic device to be increased and the life of each component to be shortened.
Therefore, in order to solve the above-mentioned problem, as disclosed in Japanese Patent Application Laid-Open Publication No. 2010-27831 (Patent Literature 1) and Japanese Patent Application Laid-Open Publication No. 2014-33062 (Patent Literature 2), the present inventors et al. developed a method in which in an electronic device in which a heat generation source is covered with a resin member having an infrared ray transmission wavelength region, a wavelength selective heat radiation material in which a multitude of microcavities forming a periodic surface fine uneven pattern are two-dimensionally arrayed is placed between the heat generation source and the resin member, thereby enhancing an infrared ray transmitting property of the resin member with which the heat generation source is covered (providing the resin member with transparency) and improving a heat radiation efficiency of the electronic device; and a wavelength selective heat radiation material used to selectively radiating heat radiation light corresponding to the infrared ray transmission wavelength region of the resin member and a method for manufacturing the same.
In the wavelength selective heat radiation material disclosed in each of Patent Literature 1 and Patent Literature 2, an opening size of each of the microcavities is approximately several μm, and the microcavities are extremely fine depressions. Therefore, in Patent Literature 1, by combining semiconductor photolithography technology and an electrolytic etching method, the microcavities are formed in the wavelength selective heat radiation material, and in Patent Literature 2, by employing nanoimprint technology, a surface fine uneven pattern, periodically repeated in a plane formed on a die, is transcribed and molded to a metal material, thereby forming the microcavities in the wavelength selective heat radiation material.
However, in the conventional technology in which the semiconductor photolithography technology and the electrolytic etching method are combined, an upper portion of a cavity wall of each of the obtained microcavities is chipped or thin-walled, thereby leading to a problem in that it is impossible to selectively radiate the heat radiation light corresponding to the infrared ray transmission wavelength region of the resin member at the emissivity as originally designed. In addition, with respect to the chipping or thin-walling of the upper portion of the cavity wall, there also is a problem in that any finding on what influence to be exerted on the radiation characteristic of the heat radiation light corresponding to the infrared ray transmission wavelength region of the resin member has not been obtained.
In the wavelength selective heat radiation material disclosed in each of Patent Literature 1 and Patent Literature 2, it is preferable that an aspect ratio of each of the microcavities is in a range of 0.8 to 3.0. This is because if the aspect ratio of each of the microcavities is below 0.8, a disadvantage in that a selective radiant intensity is reduced is caused, and on the other hand, if the aspect ratio is above 3.0, a disadvantage in that the formation of the microcavities is extremely difficult is caused.
However, in the conventional technology in which the semiconductor photolithography technology and the electrolytic etching method are combined or the nanoimprint lithography, there is a problem in that it is difficult to form microcavities each having an aspect ratio larger than 3.0 without roughening the upper portion of the cavity wall. Therefore, as the wavelength selective heat radiation material which selectively radiates the heat radiation light corresponding to the infrared ray transmission wavelength region of the resin member, a wavelength selective heat radiation material in which the microcavities each having the aspect ratio larger than 3.0 has not been known. In addition, there also is a problem in that any finding on what emissivity at which the wavelength selective heat radiation material, if the aspect ratio of each of the microcavities is larger than 3.0, is capable of selectively radiating the heat radiation light corresponding to the infrared ray transmission wavelength region of the resin member has not been obtained.